Monetisation experiment

Experiment with how we can monetise.

1. Replace sign-up with fake pay wall (allow free use if people click sign up)
2. Add donation button or two
3. Add yearly payment plan (just to cover costs)

The issue does not identify files, tests, or entry points. First inspect the existing sign-up flow and determine where donation and payment-plan functionality would fit. Done should be defined for the fake pay wall, donation option, and yearly payment plan before implementation begins.

Written by the indexing model from the issue text.